Multiple sclerosis is a prevalent disease of the central nervous system accounting for significant disability in young adults. The pathologic hallmark of multiple sclerosis consists of foci of demyelination and decreased numbers of oligodendrocytes with sparing of neurons and axons. The cellular or molecular mechanisms by which demyelination and oligodendrocyte loss occur are poorly understood. Our understanding of the oligodendrocyte response to disease hinges in part on a sufficient knowledge of normal development. The objective of this research is to identify new genes and their products important to the normal function of the oligodendrocyte. The long-term goals of this research are to provide insights into pathogenesis of demyelinating diseases and help design tools for treatment based on an expanded molecular understanding of the oligodendrocyte. The goal of the work proposed in this application is to simultaneously discover and mutate novel oligodendrocyte genes in mice through utilization of a molecular genetic screen. This aim will be accomplished using promoter trap methodology in mouse embryonic stem cells. Embryonic stem cells are near totipotent cultured cell lines derived from the pre- implantation mouse blastocyst. They can be genetically manipulated via a number of established techniques and re-implanted into donor mouse blastocycts to form chimeras where they may contribute to all tissues including the germ line. From a mutation created in vitro a chimeric animal is derived which is bred to establish animals heterozygous and homozygous for the mutation. To tag and disrupt unknown genes important to biologic processes a strategy for random insertional mutagenesis in mice termed promoter traps was developed. A DNA vector which lacks an intrinsic promoter and codes for a marker gene such as beta-galactosidase randomly inserts into the genome following transfection. When chromosomal insertion lands within a gene in the proper orientation and reading frame beta- galactosidase expression parallels that of the unknown endogenous gene. Transfected embryonic stem cells will be allowed to differentiate and oligodendrocyte-specific gene insertion will be detected by colocalizing beta-galactosidase activity with oligodendrocyte specific markers. The promoter trap vector interrupts the gene's function such that mice reconstituted from the embryonic stem cells bear a mutation in the trapped gene and the in vivo role of the interrupted gene may be assigned by examination of the phenotype of animals homozygous for the mutation.